A laser is a device that emits light through a process of optical amplification using stimulated emissions of electromagnetic radiation. The term “laser” is an acronym based on this process, and refers to “light amplification by stimulated emission of radiation”. The first lasers were built in the 1960's. Lasers differ from other sources of light in that they emit coherent light. Coherent light is a beam of photons that have the same wavelength and phase.
Lasers utilize what is referred to as a laser gain media to amplify light. A laser gain media adds optical energy to the light that traverses through the media through a process called pumping. Pumping may utilize electrical currents (referred to as electrical pumping) or light inputs (referred to as optical pumping) to generate photons. In either case, the laser gain media is pumped to an excited state, which then transitions to a rest state and emits photons. It is the state transitions that provide the amplification or gain capabilities to the laser gain media.
The amount of optical power that a laser produces may be limited by a number of factors that depend on the type of laser gain media in use. For crystal lasers, the amount of power may be limited by the heat density of the crystal. For gas lasers, the amount of power may be limited by the low energy density of the excited state of the gas.
It is desirable for certain applications that lasers operate at a high power, which can be difficult to achieve given the constraints of heat density limitations and/or energy density limitations for crystal lasers and gas lasers, respectively. Thus there is a desire to further improve the power output of lasers given these constraints.